Henri Becquerel and the Serendipitous Discovery of Radioactivity

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Antoine Henri Becquerel (born December 15, 1852 in Paris, France), known as Henri Becquerel, was a French physicist who discovered radioactivity, a process in which an atomic nucleus emits particles because it is unstable. He won the 1903 Nobel Prize in Physics with Pierre and Marie Curie, the latter of whom was Becquerel’s graduate student. The SI unit for radioactivity called the becquerel (or Bq), which measures the amount of ionizing radiation that is released when an atom experiences radioactive decay, is also named after Becquerel.

Early Life and Career

Becquerel was born December 15, 1852 in Paris, France, to Alexandre-Edmond Becquerel and Aurelie Quenard. At an early age, Becquerel attended the preparatory school Lycée Louis-le-Grand, located in Paris. In 1872, Becquerel began attending the École Polytechnique and in 1874 the École des Ponts et Chaussées (Bridges and Highways School), where he studied civil engineering.

In 1877, Becquerel became an engineer for the government in the Department of Bridges and Highways, where he was promoted to engineer-in-chief in 1894. At the same time, Becquerel continued his education and held a number of academic positions. In 1876, he became an assistant teacher at the École Polytechnique, later becoming the school’s chair of physics in 1895. In 1878, Becquerel became an assistant naturalist at the Muséum d’Histoire Naturelle, and later became the professor of applied physics at the Muséum in 1892, after his father’s death. Becquerel was the third in his family to succeed this position. Becquerel received his doctorate from the Faculté des Sciences de Paris with a thesis on plane-polarized light—the effect utilized in Polaroid sunglasses, in which light of only one direction is made to pass through a material—and the absorption of light by crystals.

Discovering Radiation

Becquerel was interested in phosphorescence—the effect utilized in glow-in-the-dark stars, in which light is emitted from a material when exposed to electromagnetic radiation, which persists as a glow even after the radiation is removed. Following Wilhelm Röntgen’s discovery of X-rays in 1895, Becquerel wanted to see whether there was a connection between this invisible radiation and phosphorescence.

Becquerel’s father had also been a physicist and from his work, Becquerel knew that uranium generates phosphorescence.

On February 24, 1896, Becquerel presented work at a conference showing that a uranium-based crystal could emit radiation after being exposed to sunlight. He had placed the crystals on a photographic plate that had been wrapped in thick black paper so that only radiation that could penetrate through the paper would be visible on the plate. After developing the plate, Becquerel saw a shadow of the crystal, indicating that he had generated radiation like X-rays, which could penetrate through the human body.

This experiment formed the basis of Henri Becquerel’s discovery of spontaneous radiation, which occurred by accident. Becquerel had planned to confirm his previous results with similar experiments exposing his samples to sunlight. However, that week in February, the sky above Paris was cloudy, and Becquerel stopped his experiment early, leaving his samples in a drawer as he waited for a sunny day. Becquerel did not have time before his next conference on March 2 and decided to develop the photographic plates anyway, even though his samples had received little sunlight.

To his surprise, he found that he still saw the image of the uranium-based crystal on the plate. He presented these results on March 2, and continued to present results on his findings. He tested other fluorescent materials, but they did not produce similar results, indicating that this radiation was particular to uranium. However, he assumed that this radiation was different from X-rays and termed it “Becquerel radiation.”

Becquerel’s findings would lead to Marie and Pierre Curie’s discovery of other substances like polonium and radium, which emitted similar radiation, albeit even more strongly than uranium. The couple coined the term “radioactivity” to describe the phenomenon.

Becquerel won half of the 1903 Nobel Prize in Physics for his discovery of spontaneous radioactivity, sharing the prize with the Curies.

Family and Personal Life

In 1877, Becquerel married Lucie Zoé Marie Jamin, the daughter of another French physicist. However, she died the following year while giving birth to the couple’s son, Jean Becquerel. In 1890, he married Louise Désirée Lorieux.

Becquerel came from a lineage of distinguished scientists, and his family contributed greatly to the French scientific community over four generations. His father is credited with discovering the photovoltaic effect—a phenomenon, important for the operation of solar cells, wherein a material produces electrical current and voltage when exposed to light. His grandfather Antoine César Becquerel was a well-regarded scientist in the area of electrochemistry, a field important for developing batteries that studies the relationships between electricity and chemical reactions. Becquerel’s son, Jean Becquerel, also made strides in studying crystals, in particular their magnetic and optical properties.

Honors and Awards

For his scientific work, Becquerel earned several awards throughout his lifetime, including the Rumford Medal in 1900 and the Nobel Prize in Physics in 1903, which he shared with Marie and Pierre Curie.

Several discoveries have also been named after Becquerel, including a crater called “Becquerel” both on the moon and Mars and a mineral called “Becquerelite” which contains a high percentage of uranium by weight. The SI unit for radioactivity, which measures the amount of ionizing radiation that is released when an atom experiences radioactive decay, is also named after Becquerel: it's called the becquerel (or Bq).

Death and Legacy

Becquerel died from a heart attack on August 25, 1908 in Le Croisic, France. He was 55 years old. Today, Becquerel is remembered for discovering radioactivity, a process by which an unstable nucleus emits particles. Although radioactivity can be harmful to humans, it has many applications around the world, including the sterilization of food and medical instruments and the generation of electricity.


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